1. Field of the Invention
The present invention relates generally to the field of diagnostic tests and, more particularly, to test devices and elements useful in the quantitative determination of an analyte having a high glucose content.
2. Brief Description of the Prior Art
Test devices in the form of test strips and similar solid phase analytical elements have become commonplace in the analysis of various types of samples, particularly biological fluids. Test strips designed for detecting sugar, i.e., glucose, in biological fluids, such as serum and urine, have been advantageous in the diagnosis of disease.
U.S. Pat. No. 4,273,868, commonly assigned herewith, discloses a composition, a test device, a method of making the test device and a process for determining glucose in a sample. The test composition comprises glucose oxidase, a peroxidatively active substance such as peroxidase, a stabilizing agent and a 3,3',5,5'-tetraalkylbenzidine indicator in an amount sufficient to rapidly produce, upon contact of the test means with a predetermined amount of a glucose-containing sample, a stable colored reaction product believed to comprise reduced and oxidized forms of said indicator in stable equilibrium. Preferably, 3,3',5,5'-tetramethylbenzidine is present in a concentration of at least about 2.6 millimoles per thousand International Units of glucose oxidase activity. One of the disclosed stabilizing agents is an interpolymer of methylvinyl ether and maleic anhydride, marketed commercially as Gantrez AN-139 by GAF Corporation. The test devices are prepared by a two-dip impregnation process where the 3,3',5,5'-tetraalkylbenzidine is impregnated in the second dip using a solution thereof prepared in an organic solvent.
U.S. Application Ser. No. 292,345, filed Aug. 13, 1981, now U.S. Letters Pat. No. 4,361,648, discloses an improvement thereover wherein a carrier is impregnated with an aqueous solution of tetraalkylbenzidine dihydrochloride and polymeric mordant and dried, then impregnated with a solution of a glucose oxidase and peroxidase, and then impregnated with a solution of a film-forming agent in a volatile solvent. Such test strip is quite satisfactory for the instrumental determination of glucose levels from 0-4000 milligrams per liter(mg/liter). Such strip, however, is not suitable for visual determination of relatively high glucose levels since the color differences are inadequate.
Bahan and Trinder in Analyst, February 1972, Vol. 97, pages 142-145, Trinder in Ann. Clin. Biochem, 6 (1969) 24-27, and Fossati et al in Clin. Chem, 26/2 (1980) 227-231 discuss using 4-aminoantipyrine as a color coupler with 3,5-dichlorohydroxybenzensulfonic acid in determining glucose levels using glucose oxidase/peroxidase system. This test is a liquid assay and is used primarily for glucose concentration between 0-4000 mg/liter. In this test, whole blood is added to a protein precipitant solution and centrifuged. The clear fluid is added to the color reagent, incubated at 30.degree. C. for 15 minutes and then the optical density is read at 515 nanometers(nm) by a spectrophotometer. This liquid system results in expected kinetics and is slow.
It is accordingly an object of the invention to provide an improved test strip which involves an atypical kinetic system, reacts quickly to permit visual quantitative glucose determination over the range from about 2000 to 8000 mg/liter, and which strip is simple and inexpensive to prepare.